Playing with this a little...

Flight 675 today is scheduled AUS-DFW 10:05-11:10a, then DFW-MEX 12:15-2:45p. Currently (10:50a), AA.com is showing it left AUS 10:20, a 15 minute delay, though it will arrive DFW early. And aa.com says estimated 1:15p departure from DFW, a one hour delay.

Texting 675 to FLYAA gets a reply showing departure times of 10:05 and 12:15. The delays shown on aa.com are not noted.

It also says to reply with flight number and airport for more detail. Texting 675 DFW gets a reply that says "AA 0675 DELAYED Departs DFW 12:15 Arrives MEX 02:45". So including the airport, the reply tells me there's a delay but it doesn't give the new current departure time.

I think this rates a #fail. I suppose it's useful if you only need a gate number, but I think I'll stick with the Google service until AA gets it fixed.

Text airline code and flight number to GOOGL (46645) and it'll reply back with current flight status, this works for most airlines. Trying it with "AA flight 675" gets the current info, including the updated 1:15 departure time. The downside to the Google service is that for a flight like this, with two legs, you get 3 messages in reply to convey all the info. That's a nuisance if you don't have unlimited text messages included in your plan.